I. Field
The present disclosure relates generally to wireless communication, and more particularly to codebook exchange in a wireless communication system, specifically a multiple access communication system.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data and so on. These systems may be multiple-access systems capable of supporting communications with multiple users by sharing the by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA), 3GPP LTE (3rd Generation Partnership Project—Long Term Evolution) systems and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more access networks, referred to herein as an access points or base stations, via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the access networks to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the access networks. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a spatial dimension. The MIMO system can provide improved performance (e.g., higher peak rates and/or coverage) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
MIMO can be used in both a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access network to extract transmit beam-forming gain on the forward link when multiple antennas are available at the access network.
Space Division Multiple Access (SDMA) systems are dependent on multiple antennae at the transmitter. SDMA relies on the spatial information of the user and categorizes the users based on their spatial location. SDMA is compatible with any multiple access schemes such as TDMA, FDMA, CDMA, etc.
Space-Division multiple access (SDMA) enables creating parallel high-capacity spatial pipes through spatial multiplexing in order to offer superior performance in radio multiple access wireless communication systems. By using MIMO technology and exploiting spatial information of the location of mobile units within the cell, SDMA techniques have been developed. The radiation pattern of the access network, both in transmission and reception is adapted to each user to obtain highest gain in the direction of the mobile user. This is often done using phased array techniques.
Precoding is a way to achieve generalized beamforming in MIMO systems. Precoding enables multiple streams of the signals from the transmit antennas with independent and appropriate weighting such that the link throughout can be maximized at the receiver output.
Precoding defines a mapping from physical antennae to the signal transmitted to a specific user, although the user is oblivious of the physical antennae pattern, and receives the signal from the effective antennae defined by the precoder. A particular mapping is defined by a precoding matrix. The columns of a precoding matrix define a set of spatial beams that can be used by the access network. The access network uses only one column (e.g., one effective antennae) of the precoding matrix in Single Input Single Output (SISO) transmissions and multiple columns (e.g., multiple effective antennae) in MIMO transmissions.
Determining effective antennae and, thus, the precoding matrix is dependent on implementation and deployment. Deployment involves many transient factors, such as the location of the access terminal, environemntal conditions, time of day and the like. Thus, for each deployment different sets of precoding matrices may be desired. The network layout, physical terrain, etc. can contribute to the choice of the set of precoding matrices. The set of such precoding matrix forms a codebook.
In view of at least the above, a need exists for a system and/or methodology for effectively and efficiently exchanging a codebook between the access network and the access terminal.